Lichens

Question 1

What type of organism is a lichen?

Answer 1

A dual organism

Question 2

Who are the two partners in a lichen symbiosis?

Answer 2

The mycobiont - fungi
The photobiont - green algae/ or cyanobacterium

Question 3

what is the most common species of mycobiont?

Answer 3

Ascomycota - around 20% form lichen

Question 4

what is the most common species of photobiont?

Answer 4

Trebouxia (green algae)
Nostoc SPP (cyanobacteria - unicellular or in chains)

Question 5

What are the respective names for green algae and cyanobacteria in lichen?

Answer 5

Phycobiont (2/3)
Cyanolichen (1/3)

Question 6

Tell me about when lichen has both a phycobiont and a cyanolichen?

Answer 6

cyanobacteria is stored in cephalodia (storing heterocysts and providing N to fungi)

Question 7

Tell me about how the photobiont provides nutrition to the mycobiont

Answer 7

the photobiont produces sugars (phycobiont = 4-6 C polyol, cyano = glucose) which it passes to the hyphae. The fungi cannot produce this alone and uses it for growth and metabolism.
Sometimes there’s an invagination into the hyphae for more effective transfer (rather than in contact cells)

Question 8

Tell me about how the photobiont can benefit in the relationship

Answer 8

Being held in the fungal thallus helps protect against desiccation.
Secondary metabolites protect against predation, pigments reduce UV exposure, high SA allows for high water/nutrient uptake

Question 9

How can sugars protect the fungi?

Answer 9

sugars are transformed in hyphae and can protect against desiccation - thought 60-80% sugars stay in mycelium as protective compound

Question 10

tell me about reproduction, and how symbiosis could be considered parasitic

Answer 10

Reproduction can be via fragmentation or asexual soredia/isidia, and then transported via wind/animals
- can be considered parasitic as the fungi dictates the reproduction of the photobiont, and can reproduce alone via ascospores (sexual and symbiosis has to be re-established)

Question 11

How are lichens used in monitoring

Answer 11

lichens are very sensitive to certain pollutants. i.e. NOx, SO2, Pb. their presence, or lack of, can suggest a pollutant in the area

Question 12

What are the 3 structural forms of lichen?

Answer 12

Crustose lichen - directly attached to the surface
Foliose lichen - leaf like and often flat against surface, attached via rhizines
Fruticose lichen - erect/ shrubby

Question 13

what percent of the biomass does the fungi dominate?

Answer 13

80-90%

Question 14

What are the two arrangements of mycobiont and photobiont in lichen?

Answer 14

heteromerous - 4 differentiated layers of thallus: upper cortex, algal zone, medulla, lower cortex
homiomerous - undifferentiated and mixed